New hope for curing blindness

Most heritable eye disease genes have now been identified. The CRUMBS IN SIGHT project seeks to understand the function of the retinal CRUMBS protein complex, required to prevent onset of progressive retinitis pigmentosa. It is time to develop cures for heritable blindness, says Dr Jan Wijnholds.

The eye brings views of the outer world into our brains and the retina is part of our central nervous system. It lets us see objects in dimmed and bright light; it tracks motion, and determines the information sent to our brains. We can live without eyes, many do, but well-functioning eyes increase the quality of life significantly. Using the newest technologies, human geneticists identify with increasing speed heritable disease genes, currently more than 160 genes for the eye. Mutations in these genes may cause retinal degenerative diseases such as age-related macula degeneration, glaucoma, diabetic retinopathy, retinitis pigmentosa or degenerative diseases affecting other eye tissues such as the lens.

There’s much still to learn about the function of eye disease genes and about how to develop cures against heritable blindness. Based at Netherlands Institute for Neuroscience Neuromedical Genetics department, Dr. Jan Wijnholds specialises in the study of retinal disease genes, generating mouse models for retinal disease, studying the function of the Crumbs protein complex, developing viral gene therapy to fight blindness caused by mutations in the Crumbs-1 gene, and exploring Müller glia progenitor cell transplantations in the eye.

Dr Wijnholds is coordinator of the EU-funded FP7 project Crumbs In Sight, which explores the function of several proteins in the Crumbs complex and studies retinal cell transplantations. He also coordinates a project financed by the Dutch medical scientific organisation ZonMw examining the development of Crumbs viral gene therapy vectors, production of clinical gene therapy vectors and promoting clinical tests in a department of Ophthalmology.

The project uses a convenient neurobiological model system (Müller glia cells and photoreceptors; fly photoreceptor cells) giving it an insight into neuron-glia interactions in general. The team has integrated high quality expertise available across Europe in order to unravel the biochemical and pathophysiological pathways that lead to retinal degeneration in progressive retinitis pigmentosa and Leber congenital amaurosis. With the results, the project will devise novel therapies, which will begin within its timeframe.

The project is divided into five key objectives addressed in five Work Packages: determination of the cellular function of Drosophila, mouse, and human CRB and CRB interacting proteins (CIPs) in polarised cells and prevention of photoreceptor death; studying the primary defects leading to loss of Müller glia cell –photoreceptor interaction in conditional Crb3 knockout retinas and embryos; studying the primary defects leading to loss of Müller glia cell – photoreceptor interaction in conditional Pals1 gene silenced (knockdown) retinas and embryos; development of Müller glia progenitor cell transplantation; and, finally, optimisation of AAV6 capsids for specific transduction of Müller glia cells, and optimisation of AAV2/6 hCRB1 clinical gene therapy vector production

The project, which complements an ongoing viral hCRB1 gene therapy programme at the Netherlands Institute for Neuroscience, aims to gain insight in the function of the Crumbs complex in regulation of Müller glia cell – photoreceptor interaction and hopes to develop safe and efficient therapeutic strategies for cures for neurosensory eye disorders.

“What the consortium has shown initially is that one of the major genes for retinitis pigmentosa is the Crumbs-1 gene,” continues Dr Winholds. “It turned out to account for three per cent of retinitis pigmentosa and 10 per cent of Leber congenital amaurosis cases. Children with these eye diseases become legally blind before their twentieth or first birthday, respectively.

“We were lucky that fruit fly geneticists already worked for several years on the Crumbs protein, and it turned out that also in this organism the protein has a function in preventing eye degeneration. From these studies and studies with similar proteins we obtained clues that directed towards a function of Crumbs-1 in polarisation of some retinal cells.”

Dr Wijnholds and his team generated a mouse model lacking Crumbs-1 that developed retinal disorganisation, and found out that the protein has an important role in maintaining adhesion between two cell types in the retina, the photoreceptor and Müller glia cells. “The photoreceptor cells are responsible for capturing the light,” he said, “and the Müller glia cells mostly serve to nurture and nurse the photoreceptor cells. Using various techniques we could prove that the full-length protein localised only to a specific region in Müller glia cells but not a similar region in photoreceptor cells. We could also show that there are two other Crumbs proteins localised to that region in photoreceptor and Müller cells, and the Crumbs proteins form a large complex with other proteins that might be essential for the function of the Crumbs proteins.

“Even though we now know that the protein is essential in the retina, where it normally is, and that it forms a protein complex, we do not know the function of the complex. Knowing the function of the complex will help tremendously in better understanding what goes wrong if Crumbs-1 is nonfunctional, and will assist us in interpreting future Crumbs gene therapy experiments in mice and men.”

The project is now studying Crumbs interacting proteins in fruit flies and cultured mammalian cells, and the loss of function in mice lacking these proteins, as well as developing viral vectors specifically for Müller glia cells that return the right level of Crumbs expression.

For more information, contact the project Coordinator, Dr Jan Wijnholds, at j.wijnholds@nin.knaw.nl or visit the project website.

Published: Friday, 9th April 2010 by Tom Freeman

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